Sea shells as money?

This is something interesting to write about.

Lately I have been doing some digging into the history of money.
I read that in the past before gold and silver was a big thing,
people used commodity's like cattle and grain.

But I also read that people have used Seashells as money,
instead of coin.

And I'm wondering to myself, how does that work?
All you have to do is go to a beach and collect some seashells
and you're rich right?

How rare are these specific seashells for them to have been
good enough to be used for money for almost 4000 years. Even until the late 20th century
in some countries.

When I try to find the answer online,
All I can find is that they where used and where they where used.
I have yet to find a web page that explains, how they where collected.
And how they turned into value.
Or maybe this is still up for debate?

My take is that like gold, People find these shells pretty,
and changed them into jewelry. Maybe this way they started trading them.

Any thoughts on this subject?